1. Field of the Invention
This invention relates generally to a drywall finishing apparatus and particularly relates to a simple, lightweight device which applies wallboard compound and wallboard tape to a wallboard joint while wiping the tape and compound, all during the same operative stroke.
2. Description of Prior Developments
Drywall or wallboard is typically fastened to the internal framework of most residential and commercial buildings. Large panels of wallboard are usually nailed to wooden "studs" to form the interior wall and ceiling surfaces. In order to provide a smooth, continuous surface across the cracks or joints formed between abutting wallboard panels, a thin covering strip of a fibrous or paper-like material is applied so as to cover the crack.
Although this covering material lacks any adhesive coating, it is referred to in the trade as wallboard "tape". In order to permanently secure this tape across the wallboard joints, an adhesive called wallboard compound or "mud" is first spread over the wall and the tape is subsequently applied to the joint. This procedure has typically required considerable effort and skill. In order to expedite this tape application procedure, various devices have been developed which simultaneously apply the tape and compound over the joint.
While these applicators generally apply tape and compound at a faster rate than that possible by manual methods using simple hand tools, they have been found to perform less than totally satisfactorily. That is, most conventional mechanized tape and compound applicators experience one or more annoying drawbacks. This has resulted in generally poor acceptance of these devices by the building trades.
A particularly bothersome drawback of several conventional compound and tape applicators is the need to wipe down the tape and compound once it has been applied to the joint. That is, these applicators are unable to adequately smooth or iron out the tape and compound so as to form a continuous, even surface during the same stroke with which they are dispensed. This condition requires an additional follow-up or clean-up procedure wherein excess compound is removed with a putty knife and irregularities such as bumps and bubbles formed beneath the tape are flattened. In practice, this type of operation requires at least two workmen--one to operate the applicator and one to follow behind to clean up the excess compound and smooth out any surface imperfections.
The irregularities referred to above are often the result of an intermittent or poorly controlled wallboard compound feed rate. In practice, an operator will often apply wallboard tape in an intermittent manner, sometimes imparting a jerking or discontinuous stop-and-go motion to the tape. With conventional applicators, such tape dispensing motion would often result in an uneven coating of compound applied to the tape. Discontinuities in the applied layer of compound would result, such as thin compound sections or dry tape sections with no compound, as well as thick, bumpy or lumpy regions.
Several devices are fed by a spring-loaded mechanism similar to those used in grease guns. These spring-loaded feed mechanisms frequently fail to provide a smooth, continuous supply of compound to the applicator nozzle. This results in a sporadic flow of compound to the tape and generates bubbles within the compound which appear as bumps or depressions beneath the tape.
Another drawback associated with presently available automated or mechanized tape and compound applicators is their cumbersome and complicated structure. An applicator loaded with compound can weigh up to 40 pounds and extend over a length of 4 to 5 feet. Use of such a device rapidly fatigues the operator. Moreover, fine finishing work is most difficult to achieve with such an awkward, heavy device.
The complicated structure of many applicators leads to frequent breakdowns and necessitates involved and costly repairs. One such applicator is known to include over 20 moving parts and is highly prone to mechanical failure.
Still another drawback of prior applicators is their inability to adequately produce a clean, "tight" corner or angle joint. That is, while somethat satisfactory results have been achieved in applying tape and compound on flat surfaces, angle joints formed along corners and at the junction of walls and ceilings have continually presented an unsolved problem to conventional applicators. The applicators are simple unable to evenly apply the tape and compound at the 90 degree angle typically formed at corners and at wall-ceiling joints.
Another problem common to prior applicators is their inability to dispense a uniform and easily controllable layer of compound upon a moving strip of tape as the tape passes through the applicator nozzle. Prior nozzles which direct the tape past and/or through a pressurized flow of compound have caused partial clogging of the compound feed paths so that only a portion of the tape is covered with compound. That is, due to an uneven balancing or application of compound feed pressure along or across different portions of the tape, the tape can be forced against the compound outlets, thereby effectively closing them.
Accordingly, a need exists for a simple, lightweight applicator which smoothly and efficiently applies a continuous and even coating of wallboard compound to a strip of wallboard tape and which simultaneously wipes down the tape so as to obviate the need for a subsequent wiping and clean-up procedure. A need also exists for a wallboard compound applicator which evenly balances and applies a pressurized flow of compound upon a moving strip of tape so that clogging of the compound feed ports is prevented.
The realization of these and various other objects, features and attendant advantages of the present invention will be more fully appreciated from the following description when considered in connection with the accompanying drawings, in which the same reference numbers designate the same or corresponding parts throughout.